[" The equation of the circle passing through "],[" the points "(1,0),(0,1)" and having the "],[" smallest possible radius is "],[[" (a) "x^(2)+y^(2)-2x-2y+1=0],[" (b) "x^(2)+y^(2)-x-y+7=0],[" (c) "x^(2)+y^(2)-x-y=0],[" (d) "x^(2)+y^(2)+x+y+1=0]]